Problem: $ C = \left[\begin{array}{rrr}0 & 1 & 2 \\ 1 & 1 & 2 \\ 0 & 2 & 1\end{array}\right]$ What is $ C^{-1}$ ?
Answer: $ = \left[\begin{array}{rrr}-1 & 1 & 0 \\ -\frac{1}{3} & 0 & \frac{2}{3} \\ \frac{2}{3} & 0 & -\frac{1}{3}\end{array}\right]$